Steps to Reproduce:
* On mediawiki vagrant virtual machine on commit fdfa0e9a6a
* Enabled roles:
* * categorytree
* * interwiki
* * monobook
* * parserfunctions
* ChessBrowser installed as additional extension in LocalSettings.php
* Run the extension test suite from the vagrant ssh: `sudo -u www-data php tests/phpunit/phpunit.php --wiki wiki --testsuite extensions`
Actual Results:
```
1) SpecialPageFatalTest::testSpecialPageDoesNotFatal with data set "RunJobs" (SpecialRunJobs Object (...))
=== Logs generated by test case
[objectcache] [debug] MainWANObjectCache using store {class} {"class":"EmptyBagOStuff"}
[wfDebug] [debug] IP: 127.0.0.1 {"private":false}
===
Headers already sent, should send headers earlier than wfHttpError [Called from MediaWiki\HeaderCallback::warnIfHeadersSent in /vagrant/mediawiki/includes/HeaderCallback.php at line 74]
/vagrant/mediawiki/includes/debug/MWDebug.php:333
/vagrant/mediawiki/includes/debug/MWDebug.php:188
/vagrant/mediawiki/includes/HeaderCallback.php:74
/vagrant/mediawiki/includes/libs/HttpStatus.php:104
/vagrant/mediawiki/includes/GlobalFunctions.php:1660
/vagrant/mediawiki/includes/specials/SpecialRunJobs.php:50
/vagrant/mediawiki/tests/phpunit/includes/specials/SpecialPageExecutor.php:108
/vagrant/mediawiki/tests/phpunit/includes/specials/SpecialPageExecutor.php:36
/vagrant/mediawiki/tests/phpunit/structure/SpecialPageFatalTest.php:33
/vagrant/mediawiki/tests/phpunit/MediaWikiIntegrationTestCase.php:416
/vagrant/mediawiki/maintenance/doMaintenance.php:99
```
Expected Results:
No error